Characterization of Carbapenemases in Extensively Drug Resistance Acinetobacter baumannii in a Burn Care Center in Iran.

The emergence of multidrug resistance (MDR) and extensively drug resistance (XDR) in Acinetobacter baumannii has made an important challenge in the treatment of infections caused by this organism. The ability of carbapenemase production is one of the main mechanisms for the emergence of MDR and/or XDR in A. baumannii. The aim of this study was to detect carbapenemase producer A. baumannii. In this study, 65 imipenem resistant A. baumannii were collected from burned patients. Biochemical identification, antibiotic susceptibility test and multiplex polymerase chain reactions for the detection of carbapenemases genes were performed. The results showed that all strains carried bla OXA-51. 83%, 12.5% and 9.23% strains harbored bla OXA-23, bla VIM and bla KPC genes, respectively. None of the isolates carried bla IMP, bla OXA-48, blaNDM-1 and bla SPM-1 genes. The results of this study indicate the emergence of Klebsiella pneumoniae Carbapenemase (KPC) in A. baumannii causing nosocomial infections in burned patients which can be important for hospital infection prevention systems in Iran.

cinetobacter baumannii has been recognized as one of the important causes of nosocomial infections in hospitalized patients, particularly in burned ones in recent years (1)(2)(3). During the past decade, in some countries, this opportunistic pathogen had high rate of infection in burned patients and was reported to be the second most common cause of nosocomial infections in burned patients (1,2,(4)(5)(6)(7). A. baumannii has been shown to acquire fast antibiotic resistance elements (8,9).
Recently, this Gram negative bacilli has shown resistance to the most available antibiotics followed by the emergence of multiple (MDR) and extensive drug resistance (XDR) strains (2,(8)(9)(10). This has partly been due to the extensive use of broad spectrum antibiotics especially in burned patients (9). Carbapenems are generally used for antibiotic therapy in infections due to MDR A. baumannii. However, the emergence of carbapenem resistant isolates has made it difficult to treat such infections (2,3,8,(11)(12)(13)(14). One of the most common and important mechanisms in carbapenem resistance in A. baumannii is their ability to produce carbapenemase enzymes (2,3,(6)(7)(8). Among the carbapenem hydrolyzing β-lactamases, class D oxacillinases (OXA type) is the most prevalent in A. baumannii strains (3,9,14). On the other hand, some studies have reported class B beta lactamases (metallo-beta lactamases) in A.
baumannii as the most prevalent carbapenemase after OXA-type (8). The significant importance is the worldwide prevalence of Klebsiella pneumoniae Carbapenemase (KPC) producers (15,16). Gram negative KPC producers can be resistant to all beta lactam antibiotics except aztreonam (17).
Most of these carbapenemases have been located in transferable genetic elements and can spread among A. baumannii and even into other Gram-negative bacilli (2,8). Therefore, the determination of carbapenemase-producing strains in healthcare
The results of antibiotic susceptibility tests indicated seven antibiotic resistance patterns (Table   3). Pattern one was observed in 55% of isolates.
Those strains were resistant to all tested antibiotics except colistin and tetracycline. In pattern two, all strains were resistant to the tested antibiotics which were observed in 25% of strains. In 20% strains, resistance to at least one of aminoglycoside antibiotics were observed according to antibiotic resistance patterns.
The Verona integron-encoded metallo-βlactamase (VIM) and KPC producing strains were observed just in two antibiotic resistance patterns.
OXA-23 and OXA-51 producing strains showed all seven antibiotic resistance patterns.
The ability of ESBL production was indicated just in one strain in combination disc method.